Pulsed and CW laser experiments in cesium and sodium-potassium vapors: The velocity dependence of 5DJ + 6PJ' going to DJ" + 6S1/2 energy pooling collisions in cesium vapor and absolute transition dipole moments of sodium-potassium 3(1)pi going to X(1)sigm

327 Pages·2008·4.07 MB·English

by  Steven J Sweeney

Pulsed and CW Laser Experiments in Cs and NaK Vapors:
The Velocity Dependence of 5Dj + 6P -> lD + 6S Energy Pooling Collisions in
f r V2
Cesium Vapor and Absolute Transition Dipole Moments of NaK 3'n —» XlX+ and
S'n —» AlT,+ Transitions using Autler-Townes Spectroscopy
by
Steven J. Sweeney
A Dissertation
Presented to the Graduate and Research Committee
of Lehigh University
in Candidacy for the Degree of
Doctor of Philosophy
in
Physics
Lehigh University
April 22, 2008
UMI Number: 3314482
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An I 22 100%
}
Date
Committee Members:
John Huennekens, Committee Chair
A. Peet Hickman
Ivan Biaggio
Gary G. DeLeo
==\
Jeffrey M. Rickman
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To my parents, for always believing in me.
iii
Acknowledgements
Obviously, the first person whom I need to thank is my advisor, Prof. John
Huennekens. The past five years have been a constant learning experience, in the lab and
outside of it, specifically the chalkboard in the hallway directly outside of the lab. I'll
always remember the countless hours he spent teaching me about not just atomic and
molecular physics, but about how to design a proper experiment and keep a lab and group
up and running. While I never had a chance to take a formal class with him, I feel like I
still learned as much from him as I possibly could have. I have the stacks of notes to
prove it, too. I'm very thankful to have had such a great teacher as an advisor, and hope
that I will be able to be as effective a teacher in my own career as he is. As sad as I am to
leave his group, it's nice to know that I will be able to work with him on future
endeavors.
I would also like to thank my other committee members, Prof. A. Peet Hickman,
Prof. Ivan Biaggio, Prof. Gary DeLeo, and Prof. Jeffrey M. Rickman, for all of the time
they invested serving on my committee. Also, Joe Zelinski, Lehigh's machinist, has
helped me immensely in keeping my experiments up and running. He has built things in
minutes that would have taken me hours, if not days, to complete on my own.
In the lab, I would like to thank Prof. Huennekens for his ability to keep the dye
laser up and running. I need to thank Dr. Tyler Morgus and Dr. Laurie Morgus for
teaching me the ins and outs of aligning the Ti: Sapphire laser, which is still (and will
probably always remain) the most involved and intricate procedure I've ever learned. I
would also like to thank Dr. Aaron Marks for helping me learn how to run the pulsed
laser setup used in the energy pooling experiment. His work on thermalizafion and initial
iv
energy pooling measurements laid the groundwork for half of this dissertation, and all his
work is greatly appreciated.
From Temple University, I would like to thank Prof. A. Marjatta Lyyra and her
group for their expertise and experience in measurements of Autler-Townes splittings
they were kind enough to share with us. Specifically, for their advice on all things
experimental, I would like to thank Dr. Ergin Ahmed and Dr. Peng Qi. I also owe a debt
of thanks to Dr. Teodora Kirova and her original program for simulating AT lineshapes.
While touring Lehigh before choosing which graduate school to attend, Prof.
DeLeo put himself on my schedule in order to talk about a new outreach grant that had
just been approved by the National Science Foundation. I am forever grateful at the
opportunity I had to serve as a NSF Teaching Fellow for my first three years at Lehigh,
spending half of my weeks bringing science demonstrations to the elementary schools of
Bethlehem. It was always fun working with him, and I can't wait to try to get my own
outreach program started.
My time at Lehigh would not have been the same without the friendships of
people like Jeff Spirko and Laura Szymanski, who I've known since I was an REU
student. Also, I'd like to thank the various members of the AMO group for so much help
and fun throughout the years, including Angela Wilkins, Dave Kashinski, Seth Ashman,
Ruth Malenda, Chris Wolfe, and Brett McGeehan, as well as Joe Junio, for all of the
hours he's spent in our office with us.
I would like to express my love and thanks to my family for all of their support
throughout the years. To my parents, Robert and Catherine, my sister, Lynda, and my
nephew, Alex, thank you, for everything. I'm who I am today because of you.
v
Finally, I would like to thank my wonderful girlfriend Carrie Sasso for all of her
love and support. She always knows the best things to say and do when I needed to relax
and keep perspective. The most stressful times (finishing this dissertation, finding a job)
were a little less so because of her. Even when Endnote kept renumbering all of my
references the night before this dissertation was due, she was able to make me laugh and
smile. Thank you, Carrie, for always bringing out the silly in me.
vi
Table of Contents
Abstract 1
1 Introduction 3
1.1 Energy Pooling Collisions 4
1.1.1 Cross-sections without Velocity Dependence 7
1.1.2 Velocity-dependent Cross Sections 9
1.1.3 Velocity Selection Using Photolysis 20
1.2 Autler-Townes Splitting and Transition Dipole Moments 23
1.2.1 Previous Experimental Techniques to Measure Transition 24
Dipole Moments
1.2.2 Fluorescence Measurements 28
1.2.3 Autler-Townes Splitting 3 6
2 General Background 47
2.1 Basics of Molecular Physics 47
2.1.1 Born-Oppenheimer Approximation 47
2.1.2 Rovibrational Structure of Diatomic Molecules 51
2.1.3 Coupling of Angular Momenta 5 7
2.1.3.1 Hund's case (a) 58
2.1.3.2 Hund's case (b) 58
2.1.3.3 Hund's case (c) 60
2.2 Transition Dipole Moments 60
2.3 Photolysis 66
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2.3.1 Photodissociation 66
2.3.2 Predissociation 68
2.3.3 Review of Early Work on Photolysis of Cs2 70
2.3.4 Determination of Molecular States Responsible for Cs Photolysis 73
2
Products
2.4 Widths and Profiles of Spectral Lines 76
2.4.1 Natural Linewidth 76
2.4.2 Doppler Width 78
2.4.3 Voigt Profile 80
2.5 Thermalization Processes 80
2.5.1 Velocity Changing Collisions 82
2.5.2 Resonance Exchange Collisions 84
2.5.3 Radiation Trapping 8 6
3 Energy Pooling Theory 89
3.1 Simple Model of 5D Atom Velocity Distribution 90
3.2 Realistic Velocity Distribution 92
3.3 Thermalization of Fast Cs(5D) Atoms 98
3.4 Energy Pooling Rate Equations 99
4 Cesium Energy Pooling Experimental Setup and Experimental Checks 106
4.1 Cesium Cell and Oven 106
4.2 Continuous Wave (CW) Laser 109
viii
4.3 Pulsed Laser Systems 113
4.3.1 Q-switched Nd: YAG Laser 114
4.3.2 Lumonics HyperDye 300 Pulsed Dye Laser 117
4.4 Experimental Pumping Scheme 119
4.5 Fluorescence Detection and Processing 121
4.5.1 Photomultiplier Tubes (PMTs) 124
4.5.2 Digitizing Oscilloscope 125
4.5.3 Photon Counter 127
4.6 Experimental Checks 129
4.6.1 Absorption Measurements 129
4.6.2 Ionization of the Cesium Vapor 133
5 Energy Pooling Experiment 141
5.1 Measured Quantities 141
5.1.1 IZ 141
or3/2
5.1.2 I (v) 141
5D
5.1.3 I (v) 150
1D
5.2 Derivation of Energy Pooling Rate Coefficient k (v) 151
EP
5.3 Energy Pooling Results 152
5.3.1 6Si/ -> 6P3/2 Pumping 152
2
5.3.2 6S1/2 -• 6P1/2 Pumping 155
5.3.3 Effect of Fine-Structure Changing Collisions on 6Pj> Populations 155
IX